Exhaust gasses, the result of internal combustion within modem piston engines, contain certain compounds, which are treated by passing them through a catalytic converter, thereby rendering them more environmentally friendly. Such engines are typically fueled by gasoline, however diesel engines are also being adapted to such catalytic converter use.
A typical catalytic converter is a unit placed within the exhaust system, such that the stream of exhaust must pass through it. It is placed near the front of the exhaust system, close to the engine, as the higher exhaust heat is beneficial to the chemical reaction within the unit.
The physical design of today's catalytic converter has not changed much in over 20 years. It typically consists of a ceramic honeycomb region, the appearance of which may be compared to a large handful of drinking straws bound together, to which slurry containing a catalyst (a mixture of precious metals) is sintered. Many such units also contain a tube inlet, to allow externally pumped air to enter and “burn” off undesirable gasses. The exhaust simply flows through the many tubes within the ceramic base and reacts to the catalyst and extra oxygen brought in via the external air. The design offers a high surface area, as it is important to expose as much exhaust to catalyst as possible, in order to convert much of the incoming volume of exhaust.